1. Field
Example embodiments relate to a semiconductor memory device and methods of operating and fabricating the same. Other example embodiments relate to a nonvolatile carbon nanotube memory device using multiwall carbon nanotubes and methods of operating and fabricating the same.
2. Description of the Related Art
The data recorded in a nonvolatile memory device may not be lost even though power supply is cut. However, because the nonvolatile memory device is characterized with a lower integration density and a lower operating speed than a volatile memory device (e.g., a DRAM), the application may be limited. Recently, while there has been proposed a nonvolatile memory device having the advantages of a typical nonvolatile memory device and the advantages of a typical volatile memory device, the application of the nonvolatile memory device has been increased.
Examples of the nonvolatile memory device, which have been recently proposed, and have the two advantages, may be FRAM, MRAM, PRAM and/or RRAM. Because the nonvolatile memory device is composed of one transistor and one storage node (e.g., a DRAM), the integration density and operating speed may not be different from the DRAM. However, with the development of information technology, the rapid spread of the internet, and the supply of various contents, the demand for memory devices having a higher memory capacity is increasing.
Therefore, a nonvolatile memory device that is an improvement on the conventional nonvolatile memory device, for example, FRAM, MRAM, PRAM and/or RRAM, in the integration density and electrical characteristics may be developed. Conventional memory devices, which have been developed up to present, may use a carbon nanotube as a storage node in order to increase the integration density.
In the conventional memory device, single-walled carbon nanotubes may be arranged in crossbar arrays. Whether the conventional memory device is in an ON state or OFF state may depend on whether two carbon nanotubes may be in contact with each other at the crosspoint of the two carbon nanotubes. The conventional memory device may be further improved in the integration density and operating speed than the typical memory devices, but the fabrication processes may be complicated. The conventional memory device may periodically prepare a separate support to support the carbon nanotube. Because the carbon nanotubes in the conventional memory device are formed of a long line shape, the carbon nanotube may be placed under periodic deformation and stress.